U.S. patent number 6,412,978 [Application Number 09/476,082] was granted by the patent office on 2002-07-02 for x-ray diagnostic apparatus.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Satoru Oishi, Naoto Watanabe.
United States Patent |
6,412,978 |
Watanabe , et al. |
July 2, 2002 |
X-ray diagnostic apparatus
Abstract
An X-ray diagnostic apparatus includes an X-ray tube for
irradiating a subject with X-rays, a rectangular planar type X-ray
detector formed by arraying a plurality of solid-state detection
elements, a supporting mechanism for supporting the X-ray tube and
the planar type X-ray detector in arbitrary postures with respect
to the subject, and a suspending mechanism for suspending the
planar type X-ray detector from the supporting mechanism. The
suspending mechanism has a rotating mechanism for rotating the
planar type X-ray detector through an arbitrary angle about a
central path of the X-rays. When necessary, the planar type X-ray
detector is rotated about the central path of the X-rays so as to
be very close to the subject. When necessary, the planar type X-ray
detector is rotated, so that the longitudinal direction of the
subject on the image and the vertical direction of the screen can
coincide with each other.
Inventors: |
Watanabe; Naoto (Nasu-gun,
JP), Oishi; Satoru (Otawara, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Kawasaki, JP)
|
Family
ID: |
11583868 |
Appl.
No.: |
09/476,082 |
Filed: |
January 3, 2000 |
Foreign Application Priority Data
|
|
|
|
|
Jan 11, 1999 [JP] |
|
|
11-004423 |
|
Current U.S.
Class: |
378/197;
378/196 |
Current CPC
Class: |
A61B
6/105 (20130101); A61B 6/4233 (20130101); A61B
6/4441 (20130101); A61B 6/587 (20130101); A61B
6/4464 (20130101) |
Current International
Class: |
A61B
6/10 (20060101); A61B 6/00 (20060101); H05G
001/02 () |
Field of
Search: |
;378/197,196,198,4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kim; Robert H.
Assistant Examiner: Kiknadze; Irakli
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. An X-ray diagnostic apparatus comprising:
an X-ray tube configured to irradiate a subject with X-rays;
a rectangular planar type X-ray detector formed by arraying a
plurality of solid-state detection elements;
a supporting mechanism configured to support said X-ray tube and
said planar type X-ray detector in arbitrary postures with respect
to the subject;
a suspending mechanism configured to suspend said planar type X-ray
detector from said supporting mechanism, said suspending mechanism
including a rotating mechanism for rotating said planar type X-ray
detector through an arbitrary angle about a central path of the
X-rays, said rotating mechanism including an actuator configured to
drive said planar type X-ray detector to rotate;
a posture detector configured to detect postures of said X-ray tube
and said planar type X-ray detector with respect to the subject;
and
a controller configured to control said actuator such that a corner
of said planar type X-ray detector does not abut against the
subject, thereby rotating said planar type X-ray detector through
an angle corresponding to the detected posture.
2. An apparatus according to claim 1, wherein said suspending
mechanism has a tilt mechanism configured to tilt said planar type
X-ray detector through an arbitrary angle with respect to the
central path of the X-rays.
3. An apparatus according to claim 2, further comprising a detector
configured to detect a tilt angle of said planar type X-ray
detector with respect to the central axis of the X-rays, and an
image processing unit configured to correct a distortion in an
image obtained by said planar type X-ray detector on the basis of
the detected tilt angle in accordance with nonlinear
transformation.
4. An apparatus according to claim 1, wherein said suspending
mechanism has a mechanism configured to move said planar type X-ray
detector close to/away from the subject.
5. An apparatus according to claim 1, wherein said rotating
mechanism has locking mechanism configured to lock rotation of said
planar type X-ray detector.
6. An apparatus according to claim 5, further comprising a lock
release switch provided to a handle of said planar type X-ray
detector.
7. An apparatus according to claim 1, further comprising an
operation switch configured to operate rotation of said-planar type
X-ray detector with said actuator.
8. An apparatus according to claim 1, wherein said controller
controls said actuator such that a longitudinal direction of the
subject on an image obtained by said planar type X-ray detector and
a vertical direction of an image display screen substantially
coincide with each other, thereby rotating said planar type X-ray
detector through an angle corresponding to the detected
posture.
9. An apparatus according to claim 8, further comprising a clutch
disconnecting switch provided to a handle of said planar type X-ray
detector.
10. An apparatus according to claim 1, further comprising a clutch
function connected to a driving shaft of said actuator.
11. An apparatus according to claim 1, further comprising an image
processing unit configured to rotate an image obtained by said
planar type X-ray detector on the basis of the detected posture
such that a longitudinal direction of the subject on the image and
a vertical direction of an image display screen substantially
coincide with each other.
12. An apparatus according to claim 1, further comprising an image
processing unit configured to rotate an image obtained by said
planar type X-ray detector on the basis of the detected
posture.
13. An apparatus according to claim 1, further comprising an image
processing unit configured to reduce an image obtained by said
planar type X-ray detector or enlarging an image display region of
a display screen, when the image extends outside said image display
region, so that the image is displayed within said image display
region.
14. An apparatus according to claim 13, wherein said image
processing unit has a function of displaying a reduction ratio of
the image or an index indicating the reduction ratio.
15. An apparatus according to claim 1, further comprising a
plurality of noncontact or contact sensors provided to or near
corners of said planar type X-ray detector, and mechanism
configured to limit rotation of said planar type X-ray detector on
the basis of outputs from said proximity sensors.
16. An apparatus according to claim 1, wherein said suspending
mechanism includes a tilt mechanism for tilting said planar type
X-ray detector by an arbitrary angle about a central path of the
X-rays.
17. An apparatus according to claim 1, wherein said suspending
mechanism includes a mechanism for moving said planar type X-ray
detector close to/away from the subject.
18. An apparatus according to claim 1, further comprising:
a collimator unit provided between said X-ray tube and the subject,
and a controller configured to control said collimator unit, when
part of an image obtained by said planar type X-ray detector
extends outside an image display region of a display screen, to
shield a region corresponding to the part of the image extending
outside said image display region.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an x-ray diagnostic apparatus in
which the imaging angle with respect to a subject has a high degree
of freedom and which is suitable for inspecting a circulatory
organ.
A conventional X-ray image diagnostic apparatus, particularly a
circulatory organ X-ray image diagnostic apparatus that can be used
during operation using a catheter or the like, is elaborated in
various manners to ensure a sufficiently large operation space for
the operator while increasing the degree of freedom of the imaging
posture with respect to the subject. For example, a C arm is
supported to be rotatable about three orthogonal rotating shafts
and slidable along rails set on the ceiling or floor surface.
FIG. 1 is a perspective view of the gantry of a conventional X-ray
diagnostic apparatus. An X-ray tube 150 and an X-ray detection
system are supported by a C-shaped (or U-shaped) arm 152 to oppose
each other through a bed 156. The arm 152 can slide along an arm
holder 153 (arrow A). The arm holder 153 is tiltably held by a
holder pillar 154 (arrow B). The holder pillar 154 is rotatably
attached to a ceiling base 157 (arrow C). The ceiling base 157 can
slide on the ceiling along rails (arrows D and E). These composite
motions A to F increase the degree of freedom of the postures of
the X-ray tube 150 and the X-ray detection system with respect to a
subject P. The mainstream X-ray detection system is a combination
of an image intensifier (I.I.) 151 and TV camera 155. A moving
mechanism is provided to move the X-ray detection system close
to/away from the subject P (arrow F). A o rotating mechanism is
provided in order to mechanically rotate the TV camera 155 by an
angle corresponding to a rotation C of the arm 152, so that the
longitudinal direction of the subject P and the vertical direction
of the display screen coincide with each other.
The I.I. 151 and TV camera 155 are heavy and large in size.
Accordingly, the gantry becomes large in size. In recent years, a
lightweight, compact planar type X-ray detector has been developed
to replace the X-ray detection system comprised of the I.I. 151 and
TV camera 155. This planar type X-ray detection system is comprised
of a phosphor film and a solid-state detection element array
arranged behind the phosphor film, converting optical signals into
electrical signals. The system may be comprised of a solid-state
detection element array directly converting X-ray signals into
electrical signals. The solid-state detection element array is
comprised of a plurality of photoelectric conversion elements, a
plurality of charge storing diodes for storing charges generated by
the photoelectric conversion elements, and a plurality of charge
read field effect transistors (FETs). X-rays are converted into
light by the phosphor film. Charges in an amount corresponding to
the intensity of the light are generated by the photoelectric
conversion elements. The charges are stored in the charge storing
diodes and are read out as imaging signals through the FETs.
The closer the planar type X-ray detector is to the subject P, the
higher the image quality. The planar type X-ray detector has a
rectangular shape, and depending on its posture, its corner may
abut against the subject P. In this case, the planar type X-ray
detector cannot be moved further closer to the subject P.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an X-ray
diagnostic apparatus in which a planar type X-ray detector can be
moved very close to the subject.
In order to achieve the above object, according to the present
invention, there is provided an X-ray diagnostic apparatus
comprising: an X-ray tube configured to irradiate a subject with
X-rays; a rectangular planar type X-ray detector formed by arraying
a plurality of solid-state detection elements; a supporting
mechanism configured to support the X-ray tube and the planar type
X-ray detector in arbitrary postures with respect to the subject;
and a suspending mechanism configured to suspend the planar type
X-ray detector from the supporting mechanism, the suspending
mechanism having a rotating mechanism for rotating the planar type
X-ray detector through an arbitrary angle about a central path of
the X-rays. When necessary, the planar type X-ray detector can be
rotated so as to be very close to the subject. When necessary, the
planar type X-ray detector is rotated, so that the longitudinal
direction of the subject on the image and the vertical direction of
the screen can coincide with each other.
There is also provided an X-ray diagnostic apparatus comprising: an
X-ray tube configured to irradiate a subject with X-rays; a
rectangular planar type X-ray detector formed by arraying a
plurality of solid-state detection elements; a supporting mechanism
configured to support the X-ray tube and the planar type X-ray
detector in arbitrary postures with respect to the subject; and a
suspending mechanism configured to suspend the planar type X-ray
detector from the supporting mechanism, the suspending mechanism
having a tilt mechanism for tilting the planar type X-ray detector
by an arbitrary angle about a central path of the X-rays. When
necessary, the planar type X-ray detector can be tilted so as to be
very close to the subject.
There is also provided an X-ray diagnostic apparatus comprising: an
X-ray tube configured to irradiate a subject with X-rays; a
rectangular planar type X-ray detector formed by arraying a
plurality of solid-state detection elements; a supporting mechanism
configured to support the X-ray tube and the planar type X-ray
detector in arbitrary postures with respect to the subject; and a
suspending mechanism configured to suspend the planar type X-ray
detector from the supporting mechanism, the suspending mechanism
having a mechanism for moving the planar type X-ray detector close
to/away from the subject. When necessary, the planar type X-ray
detector can be moved close to/away from the subject so as to be
very close to the subject.
Additional objects and advantages of the invention will be set
forth in the description which follows, and in part will be obvious
from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate presently preferred
embodiments of the invention, and together with the general
description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
FIG. 1 is a perspective view of the gantry of a conventional
circulatory system X-ray diagnostic apparatus;
FIG. 2 is a perspective view of the gantry of a circulatory system
X-ray diagnostic apparatus according to an embodiment of the
present invention;
FIG. 3 is an enlarged view of the connecting portion of a
suspension mechanism 55 and planar type X-ray detector 51 of FIG.
2;
FIG. 4 is a view showing the internal structure of a rotating
mechanism in the suspension mechanism 55 of FIG. 2;
FIG. 5 is a view showing the internal structure of another rotating
mechanism in the suspension mechanism 55 of FIG. 2;
FIG. 6 is a view showing the internal structure of a tilt mechanism
63 in the suspension mechanism 55 of FIG. 3;
FIG. 7 is a plan view of a spheroidal rotor 64 and ultrasonic
transducers 65 constituting the tilt mechanism 63 of FIG. 6;
FIG. 8 is a block diagram showing the control system of the
suspension mechanism 55 of FIG. 3;
FIG. 9 is a view showing the procedure of the rotating operation of
a planar type X-ray detector;
FIG. 10 is a block diagram of the image processing unit of FIG.
8;
FIG. 11 is a perspective view showing a side approach of this
embodiment;
FIG. 12 is a side view of FIG. 11;
FIG. 13 is a perspective view showing a side approach accompanying
a tilt of this embodiment;
FIG. 14 is a view showing distortion correction done by the affine
transformation section 26 of FIG. 10;
FIG. 15 is a block diagram showing a collimator controller 33 of
this embodiment;
FIG. 16 is a view showing the display region of a display from
which images subjected to rotation by the affine transformation
section 26 of FIG. 10 are removed;
FIG. 17 is a plan view of the collimator plates of the collimator
59 of FIG. 15;
FIG. 18 is a plan view of other collimator plates of the collimator
59 of FIG. 15;
FIG. 19 is a view showing a case wherein a reduction ratio
concerning reduction performed by the affine transformation section
26 of FIG. 10 is numerically expressed;
FIG. 20 is a view showing a case wherein the reduction ratio of
FIG. 19 is expressed by a scale;
FIG. 21 is a view showing enlargement of the scale of FIG. 20 that
accompanies a change in reduction ratio; and
FIG. 22 is a block diagram showing a case of this embodiment
wherein an image is rotated with respect to the display region of
the display by only image processing.
DETAILED DESCRIPTION OF THE INVENTION
An X-ray diagnostic apparatus according to a preferred embodiment
of the present invention will be described with reference to the
accompanying drawings.
FIG. 2 is a perspective view of the gantry of an X-ray diagnostic
apparatus according to an embodiment of the present invention. An
X-ray tube 50 is mounted on the lower end of an arcuate arm 52. A
collimator 59 having a variable-shape aperture is attached to the
X-ray radiation window of the X-ray tube 50. The arcuate arm 52 is
constructed of a C- or U-shaped member. In this embodiment, a
description will be made for a C-shaped arm 52. A square or
rectangular planar type X-ray detector 51 is supported on the upper
end of the C-shaped arm 52 through a rod-like suspension mechanism
55. The planar type X-ray detector 51 opposes the X-ray tube 50
through a bed 56. The suspension mechanism 55 is connected to the
center of the planar type X-ray detector 51.
The planar type X-ray detector 51 is comprised of a phosphor film
for converting X-rays into light, and a plurality of solid-state
detection elements arrayed on the rear surface of the phosphor
film. Each solid-state detection element is comprised of a
photoelectric conversion element for generating charges in an
amount corresponding to the light intensity, a charge storing diode
for storing the charges generated by the photoelectric conversion
element, and a field effect transistor (FET) for reading the stored
charges as an imaging signal.
A noncontact sensor 58 is attached to each of the four corners of
the planar type X-ray detector 51. When either one of the four
corners of the planar type X-ray detector 51 moves close to a
subject P by a predetermined distance or more, that is, immediately
before it comes into contact with the subject P, the corresponding
noncontact sensor 58 senses this proximity movement. When the
proximity movement is sensed, the motion of the planar type X-ray
detector 51 is limited. This will be described later in detail.
The C-shaped arm 52 is supported by an arm holder 53 to be slidable
along an arrow A. The arm holder 53 is supported by a holder pillar
54 to be tiltable along an arrow B. The holder pillar 54 is
attached to a ceiling base 57 to be rotatable along an arrow C. The
ceiling base 57 is attached to ceiling rails to be slidable along
arrows D and E.
FIG. 3 is an enlarged view of the connecting portion of the
suspension mechanism 55 and planar type X-ray detector 51 of FIG.
1. The suspension mechanism 55 has a stretching/contracting
mechanism, a rotating mechanism, and a tilt mechanism 63. The
stretching/contracting mechanism moves the planar type X-ray
detector 51 close to/away from the subject P (arrow F). The
rotating mechanism rotates the planar type X-ray detector 51 about
the central path of the X-rays (arrow G). The tilt mechanism 63
tilts the planar type X-ray detector 51 with respect to the central
path of the X-rays (arrow H). In the stretching/contracting
mechanism, an upper arm 61 is slidably inserted in a sheath pipe 60
mounted on the upper end of the C-shaped arm 52. In the rotating
mechanism, a lower arm 62 is connected to the upper arm 61 to be
axially rotatable.
A handle 14 is attached to the side surface of the planar type
X-ray detector 51. With the handle 14, the planar type X-ray
detector 51 can be manually moved conveniently. The handle 14 has a
lock release switch 15. When the manual switch (lock release
switch) 15 is pressed, all locks concerning motions (F, G, and H)
of the planar type X-ray detector 51 are released, and the planar
type X-ray detector 51 is free to move. Hence, the operator can
move the planar type X-ray detector 51 freely.
FIG. 4 is a longitudinal sectional view of the connecting portion
between the upper and lower arms 61 and 62. In the rotating
mechanism, the upper and lower arms 61 and 62 are connected to each
other through bearings 4. Rotation of the lower arm 62 with respect
to the upper arm 61 is limited within a rotational range of
.+-.45.degree.. A sprocket 7 is connected to the driving shaft of
an actuator 71, e.g., a motor, mounted on the inner wall of the
upper arm 61 through a solenoid clutch 6. The sprocket 7 meshes
with a gear 8 formed on the inner surface of the lower arm 62. A
sprocket 9 meshes with the gear 8. The rotating shaft of a position
sensor 81, e.g., a rotary encoder, is connected to the rotating
shaft of the sprocket 9.
When the solenoid clutch 6 is disconnected, the lower arm 62 is
free to rotate manually. When the solenoid clutch 6 is connected,
rotation of the lower arm 62 is locked, and the lower arm 62 cannot
be rotated manually. When the solenoid clutch 6 is connected and
the actuator 71 is driven, the sprocket 7 rotates to axially rotate
the lower arm 62. When the lower arm 62 rotates, the rotating shaft
of the position sensor 81 rotates. Hence, the rotation angle of the
lower arm 62 is detected. Exchange of electrical signals between
the upper and lower arms 61 and 62 is realized by a slip ring 13,
or a cable having such a sufficient length that it is not
disconnected even when it is twisted by a rotation of
.+-.45.degree.. A hollow direct drive motor 12 incorporating a
rotation holding bearing and a position sensor may be alternatively
used as a driving source.
FIGS. 6 and 7 show the internal structure of the tilt mechanism 63.
As the actuator of the tilt mechanism 63, an ultrasonic motor is
employed. The planar type X-ray detector 51 is connected to a
spheroidal rotor 64 held at the lower end of the lower arm 62 in a
free state. The planar type X-ray detector 51 can move freely about
the rotor 64 as the center. Three ultrasonic transducers 65 are
discretely arranged around the rotor 64. When the ultrasonic
transducers 65 vibrate, they cause friction with the rotor 64, so
as to rotate the rotor 64 in directions unique to the respective
ultrasonic transducers 65. By combining the driving operation of
the three ultrasonic transducers 65, the rotor 64 can be rotated in
an arbitrary direction. When the rotor 64 rotates, the planar type
X-ray detector 51 connected to it is tilted in a direction
corresponding to the rotating direction of the rotor 64, by an
angle corresponding to the rotation angle of the rotor 64, with
respect to the central axis of the X-rays (arrow H).
FIG. 8 shows the control system of the suspension mechanism 55 of
FIG. 3. FIG. 9 shows the procedure of the rotating operation of the
planar type X-ray detector 51. An actuator 70 is provided as a
driving source to the stretching/contracting mechanism, in the same
manner as in the actuator 71 of the rotating mechanism and an
actuator 72 of the tilt mechanism. The tilt mechanism, the rotating
mechanism, and the stretching/contracting mechanism are
respectively provided with the solenoid clutch 6 and solenoid
clutches 83 and 84 each serving also as a lock mechanism, and a
position sensor 80, the position sensor 81, and a position sensor
82 for detecting the tilt angle, the rotation angle, and the slide
amount. The operations of the actuators 70 to 72, and of the
solenoid clutches 6, 83, and 84 are controlled by a detector
positioning controller 86. The detector positioning controller 86
receives outputs from the position sensors 80, 81, and 82 as well
as an output from the noncontact sensors 58 and outputs from
position sensors 73 to 77 for detecting the tilt angle, the
rotation angle, the slide amount, and the like of the C-shaped arm
52.
The detector positioning controller 86 also receives an output from
the manual switch 15. When the manual switch 15 is pressed (SP1),
the detector positioning controller 86 performs a control operation
to disconnect the solenoid clutches 6, 83, and 84. Hence, all the
locks concerning the motions (F, G, and H) of the planar type X-ray
detector 51 are released. The planar type X-ray detector 51 is set
free to move along the arrows F, G, and H, so that the operator can
manually move it freely (mode 1). At this time, when the noncontact
sensor 58 on either one of the four corners of the planar type
X-ray detector 51 senses that this corner has moved close to the
subject P by a predetermined distance or more, the detector
positioning controller 86 connects the solenoid clutches 6, 83, and
84. This locks all motions of the planar type X-ray detector 51 to
avoid any corner of the planar type X-ray detector 51 from abutting
against the subject P. When all motions of the planar type X-ray
detector 51 are locked, the actuators 70 to 72 may be controlled
simultaneously to forcibly return the planar type X-ray detector
51.
The detector positioning controller 86 is connected to a table side
console 84 for electric power operation (mode 2) and a remote
console 85. Each of the table side console 84 and remote console 85
has three switches corresponding to the motions F, G, and H of the
planar type X-ray detector 51. When the three switches of either
the table side console 84 or remote console 85 are operated by the
operator (SP2), the detector positioning controller 86 performs a
control operation to drive the actuators 70 to 72, so that the
planar type X-ray detector 51 performs an arbitrary one of the
motions F, G, and H for an arbitrary amount with an electric power
(ST1). At this time, when the noncontact sensor 58 at either one of
the four corners of the planar type X-ray detector 51 detects that
this corner has moved close to the subject P by a predetermined
distance or more, the detector positioning controller 86 forcibly
stops the driving operations of the actuators 70 to 72 to stop
motion of the planar type X-ray detector 51. This avoids any corner
of the planar type X-ray detector 51 from abutting against the
subject P. Similarly, the actuators 70 to 72 may be controlled to
forcibly return the planar type X-ray detector 51.
The detector positioning controller 86 is connected to an auto
positioning memory 78. The positioning memory 78 stores two types
of auto positioning data (SP4) individually related to the various
postures (motions A to E) of the C-shaped arm 52 in advance. The
first auto positioning data contains information concerning
positions F to H of the planar type X-ray detector 51 to avoid any
corner of the planar type X-ray detector 51 from abutting against
the subject P when the C-shaped arm 52 is set in a certain posture.
While the posture of the C-shaped arm 52 is being changed (SP3),
the detector positioning controller 86 detects the posture of the
C-shaped arm 52 from the position sensors 73 to 77 (ST3). The
detector positioning controller 86 reads out the first positioning
data related to the posture of the C-shaped arm 52 from the
positioning memory 78, and controls the actuators 70 to 72 in
accordance with the readout first auto positioning data. Thus, the
planar type X-ray detector 51 is rotated appropriately (G), is
tilted (H), and is slid (F) so that any of its corners
automatically escapes from the subject P (modes 3-1).
The second auto positioning data contains information concerning
the rotation angle of rotation (G) of the planar type X-ray
detector 51 which is necessary for aligning the longitudinal
direction of the subject P in an image imaged by the planar type
X-ray detector 51 with the vertical direction of the image of a
display 89 when the C-shaped arm 52 is set in a certain posture.
While the posture of the C-shaped arm 52 is being changed (SP3),
the detector positioning controller 86 detects the posture of the
C-shaped arm 52 from the position sensors 73 to 77 (ST3). The
detector positioning controller 86 reads the second positioning
data related to the posture of the C-shaped arm 52 out of the
positioning memory 78, and controls the actuator 71 in accordance
with the readout second auto positioning data. Thus, the planar
type X-ray detector 51 is rotated appropriately (G), and an image
obtained by the planar type X-ray detector 51 is displayed on the
display 89 with the longitudinal direction of its subject P being
aligned with the vertical direction of the screen of the display 89
(modes 3-2).
The above four modes can be arbitrarily selected by operating the
corresponding switches of the consoles 84 and 85.
The function of aligning the longitudinal direction of the subject
P in the image with the vertical direction of the screen of the
display 89 can be realized not only by rotation of the planar type
X-ray detector 51 but also by image processing (image rotation).
This image processing will be described below.
FIG. 10 is a block diagram of an image processing unit 88 of FIG.
8. The image processing unit 88 receives an image signal from the
planar type X-ray detector 51. The image processing unit 88 has an
A/D converter 21, D/A converter 24, image memory 23, a position
memory 22, affine transformation section 26, brightness conversion
section 27, edge enhancement section 28, and nonlinear processing
section 29. The A/D converter 21 converts the image signal into a
digital signal. The D/A converter 24 converts the processed image
into an analog signal. The image memory 23 stores image data. The
position memory 22 stores posture data of the C-shaped arm 52
supplied from the detector positioning controller 86 and the
posture data of the planar type X-ray detector 51. The affine
transformation section 26 transforms the image by affine
transformation such as enlargement, reduction, and rotation. The
brightness conversion section 27 converts the brightness of the
image. The edge enhancement section 28 enhances the outline of an
internal organ or the like in the image. The nonlinear processing
section 29 corrects distortion of the image. The position memory 22
also stores the patient's name, the patient's ID number, the date
of imaging, and the imaging conditions such as the imaging mode
(the size of the field of view of the detector), the tube voltage,
the tube current, and the pulse width.
Assume that, when the arm 52 is set in a side approach state with
respect to the subject P, the longitudinal direction of the subject
P on the image is aligned with the vertical direction of the
display 89, as shown in FIGS. 11 and 12. This state is defined as
the reference.
From this reference state, when the C-shaped arm 52 is rotated
through 45.degree. (arrow C) and is tilted by 45.degree. (arrow B),
the longitudinal direction of the subject P on the image is
undesirably tilted from the vertical direction of the display 89 by
45.degree. in response to the rotation C of the C-shaped arm 52. At
this time, the affine transformation section 26 performs image
processing corresponding to a motion of inversely rotating it
through substantially 45.degree. with respect to the rotation angle
of 45.degree. of the rotation C of the C-shaped arm 52 (ST4 and ST5
of FIG. 9). Hence, the longitudinal direction of the subject P on
the image is aligned with the vertical direction of the display
89.
A general equation of this affine processing is: ##EQU1##
Note that (x, y) represents coordinates before conversion, (X, Y)
represents coordinates after conversion, A, B, C, and D are
conversion coefficients concerning rotation (enlargement or
reduction), and E and F are conversion coefficients with which
translational motion is performed. Transformation of equation (1)
to apply it to a case wherein the image is rotated by a rotation
angle .theta. yields: ##EQU2##
When the planar type X-ray detector 51 is tilted, the X-ray
enlargement ratio becomes nonuniform within the detection plane of
the planar type X-ray detector 51 in accordance with a change in
distance from the focal point of the X-ray tube 50. Therefore, the
image distorts as shown in the left side of FIG. 14. In this case,
as shown in the right side of FIG. 14, in order to solve this
distortion, the nonlinear processing section 29 subjects the image
to a nonlinear process to set the X-ray enlargement ratio constant
on the basis of the direction of tilt and the tilt angle of the
planar type X-ray detector 51.
The flow of the inspection process with the arrangement of this
embodiment will be described. The operator sets the arm 52 in such
a position and direction that the target portion of the subject P
can be observed easily. This posture is output from the position
sensors 73 to 77. The detector positioning controller 86 rotates
the planar type X-ray detector 51 in accordance with the second
auto positioning data related to the posture read from the position
sensors 73 to 77. In this rotation, when rotation of the planar
type X-ray detector 51 is stopped midway in accordance with the
outputs from the noncontact sensors 58, a message indicating that
rotation of the planar type X-ray detector 51 does not reach the
rotation angle represented by the second auto positioning data is
displayed. Upon reception of this message, the operator manually
and additionally rotates adds rotation of the planar type X-ray
detector 51. When rotation of the planar type X-ray detector 51
reaches the rotation angle represented by the second auto
positioning data, this fact is displayed.
After the postures of the C-shaped arm 52 and planar type X-ray
detector 51 are set in this manner, imaging is performed with the
preset X-ray conditions. The obtained image is converted by the A/D
converter 21 into digital signals. The converted image data is
distortion-corrected by the nonlinear processing section 29, and is
stored once in the image memory 23 comprising a hard disk and RAID.
An image distortion is corrected on the basis of the rotation angle
of the planar type X-ray detector 51 obtained from the imaging
condition memory 22. The corrected image is subjected to affine
transformation by the affine transformation section 26, edge
enhancement transformation by the edge enhancement section 28,
density (density gradation) conversion by the brightness conversion
section 27, and the like, if necessary, is then converted into
analog signals by the D/A converter 24, and the image is displayed
on the display 89.
As described above, when the image is rotated such that the
longitudinal direction of the subject P on the image is aligned
with the vertical direction of the display 89, portions 41a of the
image extend outside a display region 40, as shown in FIG. 16.
These excluded portions 41a are not displayed, and only a central
portion 41b other than the excluded portions 41a is displayed.
X-rays corresponding to the portions 41a cause unnecessary
exposure. In order to shield these portions, a collimator
controller 33 in FIG. 15 controls a collimator 59 to form an
aperture in it.
The flow of inspection process with this arrangement will be
described. The operator sets the arm 52 in such a posture that the
target portion can be observed easily. The preset posture is
detected by the position sensors 73 to 77. The detector positioning
controller 86 rotates the planar type X-ray detector 51 on the
basis of the detected posture. When the longitudinal direction of
the subject P and the vertical direction of the display are
misaligned from C each other due to this rotation, the image is
rotated. In this case, the rotation angle .theta. through which the
image is rotated in this image processing is stored. The collimator
controller 33 changes the shape of the aperture of the collimator
59 so that regions corresponding to the portions 41a excluded from
the display region 40 are not irradiated with the X-rays.
FIG. 17 shows the arrangement of the collimator plates of the
collimator 59. In the collimator 59, a plurality of collimator
plates 37a are provided to be radially movable about the X-ray axis
as the center. In the case of FIG. 17, a total of eight collimator
plates 37a are provided. When the image is rotated by image
processing, the collimator controller 33 moves the respective
collimator plates 37a on the basis of the rotation angle .theta. to
shield portions corresponding to the portions 41a that are not
displayed. This avoids unnecessary exposure. The collimator 59 may
be formed by combining hollow square collimator plates 38a and 38b,
as shown in FIG. 18. The collimator controller 33 rotates only one
collimator plate 38b in the same direction and through the same
angle as in rotation of the rotation angle .theta. done by image
processing.
To eliminate the portions 41a that are not displayed, when the
image is rotated, it is sometimes reduced simultaneously. In this
case, the degree of reduction is displayed in character or numeric
indication 43 as a reduction ratio index on the display region 40,
as shown in FIG. 19, so that it can be recognized easily.
Alternatively, as shown in FIGS. 20 and 21, a scale bar 44
indicating the reference length of the reduction ratio index is
displayed simultaneously. The scale bar 44 stretches or contracts
in accordance with the reduction ratio. Alternatively, the image
may not be reduced or the display region may not be enlarged in
this manner, but a scroll bar (not shown) may be displayed on the
display region 40, and the image itself may be moved such that
portions excluded from the display region 40 can be seen.
If only the longitudinal direction of the subject P in the image
need be aligned with the vertical direction of the screen, a simple
arrangement as shown in FIG. 22 suffices.
Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects
is not limited to the specific details and representative
embodiments shown and described herein. Accordingly, various
modifications may be made without departing from the spirit or
scope of the general inventive concept as defined by the appended
claims and their equivalents.
* * * * *